The NIH Animal Genetic Resource (NIHAGR) maintains a large number of unique rat genotypes used as models of normal and disease processes in man. Effective management of this resource would be facilitated by the development of embryo cryopreservation procedures for long-term banking. In order to develop banks of cryopreserved germ plasm from laboratory, protocols for each step of the embryo banking and rederivation process must be established. These would include the preparation and mating of embryo donor females, embryo collection, cryopreservation, thawing, and embryo transfer. Previous studies indicate that superovulation procedures developed for laboratory mice are not as effective when applied to laboratory rats. The principal objective of this project is evaluate treatment with an analog of gonadotropin releasing hormone (GnRH-a) as an alternative approach to synchronize estrus cycles for embryo collection and timed pregnancy.